Violet attended Le Conte Junior High School and Hollywood High School. In 1928 Violet was approached by silent screen actress Nance O'Neil who offered her speech and movement lessons, and with her sister Jean's help, Violet soon entered the movies. She secured a contract with Pathé where she was featured in many short subjects under the name Marilyn Morgan.

In 1931, after appearing in a number of short films, Marsh landed one of her most important roles in Svengali opposite John Barrymore. Marsh was chosen by Barrymore, himself, for the role of "Trilby". Barrymore, who had selected her partly because she resembled his wife, coached her performance throughout the picture's filming. Svengali was based on the 1894 novel Trilby written by George du Maurier.

A popular play, likewise entitled Trilby, followed in 1895. In the film version, which Warner Bros. had retitled Svengali, Marsh plays the artist's model Trilby, who is transformed into a great opera star by the sinister hypnotist, Svengali. The word "Svengali'" has entered the English language, defining a person who, with sometimes evil intent, tries to persuade another to do what he desires.

In 1932, in the midst of a grueling work schedule, Marsh left Warner Bros. and took several film offers in Europe which lasted until 1934. She enjoyed working in England and Germany, as well as vacationing several times in Paris. Back in the United States, she appeared as the heroine, Elnora, in a popular adaptation of the perennial favorite A Girl of the Limberlost (1934).